1. Field of the Invention
This invention relates curable compositions and, more specifically, compositions containing 2-cyanoacrylic acid esters which are main ingredients of 2-cyanoacrylic ester type instant curing adhesives utilized broadly for bonding, repairing and covering of products in various field of industries. Curable composition can be utilized in those fields of industries where such instant adhesives have been used broadly, as well as in beauty parlor or like other service area and further in home uses.
2. Description of Related Art Including Information Disclosed under 1.97-1.99
Upon contact with the moisture in the atmosphere or a trace quantity of water adsorbed to the surface of a material to be coated with adhesives, 2-cyanoacrylic acid esters rapidly polymerize to cure and show excellent adhesive performance under ambient temperature and, accordingly, they have been widely used for instant adhesiveness for the bonding of plastic, rubber, glass and metal.
Meanwhile, various attempts have been made for the addition of powdered organic or inorganic compounds in order to improve the properties of curing products of 2-cyanoacrylic acid esters to increase the number of uses of adhesives and also of paints and coating or potting agents by utilizing the above-mentioned properties of 2-cyanoacrylic acid ester.
For instance, it has been attempted to utilize the instant curing property of 2-cyanoacrylic acid esters as electroconductive adhesives, or as substitutes for soldering and electroconductive paints for use in the fixing of lead wires to contacts, manufacturing of circuits or painting for electromagnetic wave shields in electronic or electrical industries by the addition of electroconductive powder to 2-cyanoacrylic acid ester.
Further, attempts have been made to add a pigmenting agent, for coloration, to 2-cyanoacrylic acid ester to facilitate the identification of various kinds of adhesives thereby preventing errors in coating them and, further, utilize them as paints and, particularly, rapid curing paint (refer to Japanese Patent Publication No. Sho 46-35250, Japanese Patent Laid-Open No. Sho 52-65531 and Japanese Patent Publication No. Sho 55-11685).
Furthermore, it has also been tried to add various kinds of powders of high polymers or inorganic compounds in order to improve the peeling-strength and impact shocks which are important as the properties of the adhesives (refer to Japanese Patent Laid-Open No. Sho 60-199084).
However, the instantaneous curing property of 2-cyanoacrylate esters improves as the purity and such improves instantaneous curability is reduced as additives are added. Further, the storage stability often becomes poor. Accordingly, it has been extremely difficult and rarely successful to improve the properties of 2-cyanoacrylic acid ester by adding additives.
While on the other hand, various kinds of stabilizers have been studied for providing satisfactory storage stability without damaging the instantaneous curability of 2-cyanoacrylic acid ester. For such stabilizers, there have been proposed, for example, acidic gases such as SO.sub.2, NO and HF or solid acids such as phosphor pentoxide, antimony pentoxide, picric acid and ferric chloride (refer to U.S. Pat. Nos. 2,467,926, 2,467,927, 2,721,858, 2,756,251, 2,763,677, 2,765,332 and 2,794,788), phosphor pentoxide, acetic acid, acrylic acid, methacrylic acid, itaconic acid, SnCl.sub.4, complex salts of boron trifluoride with ether, carboxylic acids, ketones and other similar oxygen atom-containing compounds, ferric chloride and other Lewis acids (refer to U.S. Pat. Nos. 2,912,454 and 2,926,188), anhydrous sulfuric acid or benzene sulfinic acid (Japanese Patent Publication No. Sho 45-2010), sulfuryl chloride (Japanese Patent Publication No. Sho 45-35291), sultone (Japanese Patent Publication No. Sho 45-41520, 47-50213), aromatic sulfonic acid (Japanese Patent Publication Nos. Sho 46-13729, 48-10379, British Patent No. 1301645 and U.S. Pat. No. 3,652,635), non-volatile acid with pKa less than 3 (Japanese Patent Publication No. Sho 46-37278), combination of aromatic sulfonic acid with acidic gas such as SO.sub.2, NO and HF (Japanese Patent Publication Nos. Sho 48-13334 and 48-16904), boron trifluoride--phenol complex salt, boron trifluoride--carboxylic acid complex salt, boron trifluoride--ether complex salt (Japanese Patent Publication No. Sho 56-52949), trichloro acetic acid (Japanese Patent Laid-Open No. Sho 49-31619), oxonium compounds and phosphonium compounds (Japanese Patent Publication No. Sho 56-53593), etc. as well as various other compounds.
The present inventors have made various studies of stabilizers, including those as described above, capable of attaining satisfactory storage stability of curable compositions, in which organic or inorganic powder is added and dispersed in order to improve the properties of 2-cyanoacrylic acid esters, without damaging the instantaneous curability thereof and have accomplished this invention based on the findings that the foregoing purpose can be attained by the combination of specific stabilizers, that is, by the combined use of an acidic substance and a basic substance as the stabilizer.